REP Geothermal and Hydropower 4 — Questions and Answers
Question 1: Which type of hydropower turbine is most appropriate for very high head applications (above 300 m)?
- Kaplan turbine
- Bulb turbine
- Pelton turbine (Correct answer)
- Cross-flow (Banki-Michell) turbine
Correct answer: Pelton turbine
Pelton turbines are impulse turbines designed for very high head, low-flow sites, using jets of water striking buckets on the runner to convert kinetic energy to mechanical energy.
Question 2: What environmental mitigation measure is commonly required at hydropower dams to support fish migration?
- Installation of submerged ozone generators to improve water quality
- Construction of fish ladders or bypass channels around the dam (Correct answer)
- Periodic reservoir drawdown to expose spawning gravel beds
- Deployment of acoustic deterrents to redirect fish away from turbines
Correct answer: Construction of fish ladders or bypass channels around the dam
Fish ladders (fishways) and bypass channels are required at many dams to allow migratory fish such as salmon to pass upstream past the barrier, a key condition in FERC licensing.
Question 3: Geothermal gradient refers to which physical measurement?
- The rate of increase in temperature with depth below the Earth's surface (Correct answer)
- The slope of the terrain above a geothermal field
- The pressure differential between surface and reservoir fluid
- The electrical resistivity profile of subsurface rock layers
Correct answer: The rate of increase in temperature with depth below the Earth's surface
Geothermal gradient is the rate of temperature increase per unit depth in the Earth's crust, typically about 25–30°C/km globally, but much higher in volcanic and tectonic regions suitable for energy extraction.
Question 4: A small hydropower developer wants to avoid full FERC licensing. Which project size typically qualifies for the simplified 'exemption' process?
- Projects over 100 MW
- Projects between 10 MW and 80 MW
- Projects of 5 MW or less at existing dams or natural water features (Correct answer)
- Projects using only tidal or wave energy
Correct answer: Projects of 5 MW or less at existing dams or natural water features
FERC offers a simplified exemption process for small hydropower projects of 5 MW or less at existing dams or natural water features, reducing regulatory burden while maintaining environmental review.
Question 5: In geothermal energy, what is the function of a 'separator' in a flash steam plant?
- It removes dissolved minerals from reinjection water before disposal
- It separates steam from liquid brine after pressure reduction so steam can drive the turbine (Correct answer)
- It isolates the turbine from the generator to prevent electrical feedback
- It filters particulates from condensed steam before it is reinjected
Correct answer: It separates steam from liquid brine after pressure reduction so steam can drive the turbine
In flash steam plants, the separator uses centrifugal force to separate steam from two-phase geothermal fluid after pressure is reduced, directing steam to the turbine and brine to reinjection or further flashing.
Question 6: What is the primary advantage of underground (cavern) pumped-storage hydropower over conventional surface reservoir pumped storage?
- Lower construction cost per MW of storage capacity
- Reduced land use and surface environmental impact (Correct answer)
- Higher round-trip efficiency due to shorter water travel distance
- Elimination of the need for a lower reservoir
Correct answer: Reduced land use and surface environmental impact
Underground pumped-storage systems use excavated caverns as the lower reservoir, dramatically reducing surface land use, visual impact, and siting constraints in areas without suitable natural topography.
Question 7: Which geophysical survey method is most commonly used to locate subsurface geothermal reservoirs before drilling?
- Airborne LiDAR topographic mapping
- Magnetotelluric (MT) resistivity surveying (Correct answer)
- Ground-penetrating radar (GPR) profiling
- Gamma-ray spectroscopy from satellite imagery
Correct answer: Magnetotelluric (MT) resistivity surveying
Magnetotelluric surveying measures natural electromagnetic fields to map subsurface electrical resistivity, helping identify conductive hydrothermal fluids and reservoir boundaries before expensive drilling.
REP Geothermal and Hydropower 4
Which type of hydropower turbine is most appropriate for very high head applications (above 300 m)?